1. Field of the Invention.
The present invention relates to the production of meso-1,2,3,4-tetrachlorobutane, which compound is of established utility in the production of 2,3-dichlorobutadiene. More particularly, this invention relates to a method for preparing meso-1,2,3,4-tetrachlorobutane from trans-1,4-dichlorobutene-2 in a liquid phase chlorination process.
2. Description of the Prior Art.
In preparing meso-1,2,3,4-tetrachlorobutane from dichlorobutenes in a liquid phase chlorination process, there are produced, in addition to the desired meso-isomer, the dextrorotatory and levorotatory 1,2,3,4-tetrachlorobutanes (the racemic mixture is referred to as dl-isomer) and a proportion of chlorinated materials designated as heavy ends. These heavy ends are generally more highly chlorinated products such as the pentachlorobutanes. The formation of dl-isomer and heavy ends is undesirable in that these materials represent a yield loss and are undesirable contaminants in the desired meso-1,2,3,4-tetrachlorobutane product.
Known methods for preparing meso-1,2,3,4-tetrachlorobutane from dichlorobutenes in a liquid phase chlorination process have been generally unsatisfactory. Noncatalytic processes, such as those disclosed in Japanese Pat. No. 38,802 (1970) and in the Journal of the American Chemical Society 73, 244-6 (1951), require extremely low temperatures of from 0.degree.C. to about -30.degree.C. and are, therefore, generally undesirable economically. Known processes for carrying out the chlorination reaction at moderate temperatures in the range of from about 50.degree.C.-150.degree.C. involve the use of a catalyst. See, for example, the process disclosed in French Pat. No. 1,401,077 (titanium tetrachloride catalysts), French Pat. No. 1,401,078 (pyridine catalysts), and U.S. Pat. No. 2,445,729 (ferric chloride or antimony pentachloride catalysts). All of these processes are generally unsatisfactory in that there are produced a large proportion of heavy ends material and an undesirably large proportion of the dl-isomer. These catalytic processes are additionally undesirable due to the presence of the metallic catalyst in the reaction product.